JPH0462667B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a reversal development method for obtaining a reversal toner image by depositing a one-component magnetic toner on the uncharged area of an electrostatic latent image formed on the surface of an image carrier. The present invention relates to a reversal development method using magnetic toner that can be fixed under pressure. [Prior Art] In recent years, as information processing equipment has become more sophisticated and diversified, there has been a demand for diversified output formats and faster speeds, and non-impact electrophotographic printers have been developed. The recording principle of the printer described above is similar to that of general electronic copying machines, in which an electrostatic latent image formed on the surface of an image carrier is developed and then transferred to plain paper. In printers, information from a computer is written on the uniformly charged surface of an image carrier using a laser beam or the like, and in order to attach toner to the written area, that is, the exposed area, it is necessary to perform reversal development. The developer used in the above reversal development is generally a two-component developer consisting of a magnetic carrier and a toner. Although this method enables electrostatic transfer of toner images onto plain paper and provides high-quality printer images, it requires a means to maintain a constant mixing ratio of carrier and toner. Therefore, there is a drawback that the developing device becomes larger and more complicated, and the carrier needs to be replaced periodically. In order to overcome these drawbacks, there is a method of developing an electrostatic latent image using a one-component developer consisting only of magnetic toner particles. In the above reversal development method using magnetic toner, a DC bias voltage of the same polarity as the electrostatic latent image is applied to a conductive sleeve holding magnetic toner having a charge of the same polarity as the electrostatic latent image. This causes the toner to adhere to the non-image area. Further, when a toner image obtained by development is electrostatically transferred onto a transfer sheet, an insulating magnetic toner having high electrical resistance is generally used. [Problems to be solved by the invention] When reversal development is performed by charging the charged insulating magnetic toner as described above to the same polarity as the electrostatic latent image, the image quality is lower than that using a two-component developer. The reality is that it is inferior to what was done. In other words, when using magnetic toner that is charged to the same polarity as the electrostatic latent image, results equivalent to those using the two-component developer described above can be obtained in terms of image density, but in terms of resolution. There is a problem in that it is not sufficient and dust tends to occur around the image. The present invention solves the above-mentioned problems and aims to provide a reversal developing method that uses magnetic toner, has high resolution, and does not generate dust around the image. It is something. [Means for Solving the Problems] In order to solve the above problems, the following technical means were adopted in the present invention. That is, A. An electrostatic latent image is formed on the surface of an image carrier, and a non-magnetic conductive sleeve, which is disposed opposite to the surface of the image carrier and has a magnetic field generating member inside, is mainly composed of resin and magnetic powder. A magnetic toner is supplied, the magnetic toner is conveyed toward the image carrier surface by relative rotation between the sleeve and the magnetic field generating member, and a DC voltage is applied to the sleeve to form a non-image of the electrostatic latent image. In the reversal development method in which the magnetic toner is attached to the portion. B. Negative charging characteristics of the image carrier. C. The magnetic toner is capable of cold pressure fixing and has positive charging characteristics. D. Applying a negative DC voltage to the sleeve.
This is a technical measure taken. [Operation] FIG. 1 is a sectional view of essential parts showing an example of a developing device for carrying out the present invention. In the figure, reference numeral 1 denotes a photoreceptor drum, which consists of a photoconductive layer 1a holding an electrostatic latent image (indicated by the symbol - in the figure) and a conductive substrate 1b electrically grounded, and is directed in the direction of arrow W. Rotatably installed. Next, 2 is a toner tank which stores toner 3. A sleeve 4 is rotatably provided in the lower part of the toner tank 2 facing the photoreceptor drum 1, and a permanent magnet member 5 having a plurality of magnetic poles on its surface is coaxially arranged in the sleeve 4 and arranged in the direction indicated by the arrow X.
It is provided so that it can rotate independently in the direction. Reference numeral 6 denotes a doctor blade, which is provided so as to face the surface of the sleeve 4 so as to be able to come in and out at will, and is used to remove the toner 3 that moves on the sleeve 4.
Regulate the thickness of Next, the sleeve 4 is made of a non-magnetic and conductive material such as austenitic stainless steel or aluminum alloy, and is electrically connected to a DC power source 7 having negative polarity. A reversal development method using the above configuration will be described. First, by rotating the sleeve 4 and the permanent magnet member 5 relative to each other, the toner 3 contained in the toner tank 2 is pulled out onto the sleeve 4 and conveyed from the doctor gap d to the developing gap D in the direction of arrow Y. Toner 3 is in photoconductive bath 1
It has a property of being positively charged with a polarity opposite to that of the electrostatic latent image formed on a, and becomes positively charged by contact between the sleeve 4, the doctor blade 6, or the toner 3 during the conveyance process. When the positively charged toner 3 reaches the development area,
It adheres to the non-image areas of the photoconductive layer 1a to form a toner image. Next, this toner image reaches a transfer position by the rotation of the photoreceptor drum 1, and by applying a positive electric field with a polarity opposite to that of the electrostatic latent image from the back side of the transfer sheet (not shown), the toner image is transferred to the transfer position. transcribed on top;
Then, it is fixed by pressure fixing means. In the reversal development method of the present invention, since magnetic toner is used which is charged with a polarity opposite to that of the electrostatic latent image, the magnetic toner is thought to adhere to the image area of the electrostatic latent image. According to experiments conducted by the present inventors, it has been confirmed that the electrostatic latent image clearly adheres to the non-image area as described above, and the reproducibility is also sufficient. The reason why high quality images can be obtained by the present invention is as follows.
Although the details are unknown, it is assumed that the reason is as follows. In the process of conveying magnetic toner on the sleeve,
As described above, most toner particles are positively charged and have a positive charge. When this magnetic toner reaches the development area and enters the electric field of the electrostatic latent image,
Charges in the toner move according to the direction of the electric field, and toner particles near the interface with the photoreceptor, where the electrostatic latent image potential is low, become negatively charged. As a result, negatively charged toner particles adhere to non-image areas of the electrostatic latent image, resulting in a reversed image. Therefore, in the past, a magnetic toner charged to the same polarity as the electrostatic latent image was used, which caused an overdevelopment state. That is, too much toner adheres to the surface of the photoreceptor, resulting in dust. On the other hand, according to the present invention, only the toner near the interface with the photoreceptor has a charging polarity that contributes to development, so it is thought that overdevelopment can be suppressed and dust generation can be prevented. The magnetic toner used in the present invention has a triboelectric charge amount of 2 to 2 when measured by a blow-off method.
20μc/g, and the charging voltage on the sleeve is 5~
Preferably it is 60V. That is, when the amount of triboelectric charge and the charging voltage become excessive, the image density decreases, while when they are insufficient, fog increases, both of which are disadvantageous. Next, the magnetic powder constituting the magnetic toner includes alloys or compounds containing ferromagnetic elements such as iron, cobalt, and nickel, including ferrite and magnetite, and other materials that have been made ferromagnetic by heat treatment or some other treatment. Various alloys such as those shown may be used. These ferromagnetic materials are several μm to several tens of μm
Since it is contained in a toner having a particle size of 0.02 to 3 μm, it is desirable that the average particle size is 0.02 to 3 μm. Therefore, the amount contained in the toner is 30 to 70% of the total amount of toner.
It is desirable to set it as weight%. If it is less than 30% by weight, the magnetic force of the toner decreases and it becomes easy to scatter from the sleeve, while if it exceeds 70% by weight, the resin content becomes extremely low and the fixing properties are deteriorated, which is disadvantageous. Next, the magnetic toner used in the present invention can be fixed under cold pressure, and for example, the following resins are used. Namely, higher fatty acids, higher fatty acid metal salts, higher fatty acid derivatives, higher fatty acid amides, waxes, rosin derivatives, alkyd resins, epoxy-modified phenolic resins, natural resin-modified phenolic resins, amino resins, silicone resins, polyurethane, urea resins. , polyester resin, copolymerized oligomer of acrylic acid or methacrylic acid and long-chain alkyl acrylate, copolymerized oligomer of styrene and long-chain alkyl acrylate, long-chain alkyl methacrylate, polyolefin,
Examples include ethylene-vinyl acetate copolymers, ethylene-vinyl alkyl ether copolymers, maleic anhydride copolymers, petroleum residues, rubbers, and the like. Any of the above resins can be arbitrarily selected and mixed as desired, but those having a glass transition point exceeding 40° C. are effective in order not to reduce the fluidity when formed as a toner. In addition to the above, various pigments and/or additives used in general dry developers can be added. However, the content based on the total amount of the toner is suitably less than 10% by weight, taking into consideration the electrical properties of the toner. Pigments that can be used include, for example, carbon black, aniline blue, calco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chlorad, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal and and mixtures thereof. Note that when the magnetic powder itself is colored, such as magnetite, there is no need to add it. In addition, when using carbon flux, in order not to reduce the insulation properties of the toner, it is necessary to
It is desirable to contain it in a range of 5 parts by weight. Next, the magnetic toner used in the present invention can be manufactured from the above-mentioned materials by a known method such as a pulverization method or a spray drying method. The average particle size of the toner to be produced is preferably in the range of 5 to 30 μm, preferably 10 to 20 μm. The electric resistance or fluidity can be adjusted by adding conductive particles such as carbon black or tin oxide or additives such as silica powder to the toner particle surface after classification. [Examples] The present invention will be specifically explained below using Examples, but the present invention is not limited to these Examples. Polyethylene wax (manufactured by Mitsui Petrochemical Industries)
HIWA×200P) and ethylene-vinyl acetate copolymer (ACP400 manufactured by Allied Chemical Co., Ltd.) mixed at a weight ratio of 7:3, magnetite (EPT500 manufactured by Toda Industries), and a positive charge control agent (Bontron No. manufactured by Orient Chemical Co., Ltd.). .1) were dry mixed according to the formulation shown in the table, and heated and kneaded in a kneader at a temperature of 200°C. The resulting kneaded product was cooled and solidified, and then ground into particles of 20 μm or less using a jet mill. Next, this pulverized powder was put into a super mixer, and 0.1 to 0.5 parts by weight of finely powdered silica (R972 manufactured by Nippon Aerosil Co., Ltd.) was added and mixed. The mixed powder was heat-treated by introducing it into a hot air stream at 120°C, and then classified using a zigzag classifier to obtain magnetic toner No. 1 with a particle size distribution of 5 to 20 μm. 1 to 4 were obtained. The triboelectric charge amount (hereinafter referred to as TEC) and surface potential of these magnetic toners are shown in the table. The TEC of the above-mentioned magnetic toner was measured using a commercially available blow-off powder charge measuring device (Toshiba Chemical TB-
200) under the following conditions. Carrier (Japan Iron Powder Z-200) 10g and toner 0.5g
was placed in a plastic container with an outer diameter of 40 mmφ, and rotated for 10 minutes using a flow surface angle measuring device. A 200 mg sample was taken from the resulting mixture and placed in a container using a 325 mesh sieve. The charge amount is measured using a charge measuring device under the conditions of a blow pressure of 1.0 Kg/mm ² and a blow time of 40 seconds. In addition, the charging voltage of the toner, that is, the surface potential is the second
Measure with the equipment shown in the figure. In the same figure,
8 is a non-magnetic sleeve (outer diameter 50mmφ), 9 is a permanent magnet member (outer diameter 46mmφ, length 150mm, 12 poles symmetrical magnetization,
The magnetic flux density on the sleeve is 1000 G), 10 is a surface electrometer (Trek 344), and 11 is a probe. After adjusting the gap g between the sleeve 8 and the probe 11 to 5 mm, 3 g of toner was supplied onto the sleeve 8, and the surface potential of the toner was measured when the permanent magnet member 9 was rotated at 1000 rpm for 1 minute. do. Next, magnetic toner with different TEC and surface potential
No.．． Examples 5 to 7 were produced under the same conditions as in the above example. In addition, No. Magnetic toner No. 5 differs from other toners in that it uses a negative charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.).

〔Effect of the invention〕

Since the reversal developing method of the present invention has the structure and operation described above, it is possible to obtain a high-quality image, and in particular, to obtain a reversal image that has high resolution and does not generate dust around the image. effective.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a developing device for carrying out the present invention, and FIG. 2 is a sectional view showing a toner surface potential measuring device. 1: Photosensitive drum, 3: Toner, 4: Sleeve, 5: Permanent magnet member.

Claims (1)

[Scope of Claims] 1. An electrostatic latent image is formed on the surface of an image carrier, and resin and magnetic powder are placed on a non-magnetic conductive sleeve that is disposed opposite to the surface of the image carrier and has a magnetic field generating member inside. The magnetic toner is supplied as a main component, and the magnetic toner is conveyed toward the surface of the image carrier by relative rotation between the sleeve and the magnetic field generating member, and a DC voltage is applied to the sleeve to form the electrostatic latent image. In the reversal development method in which the magnetic toner is attached to a non-image area of the image carrier, the image carrier has a negative charging characteristic, the magnetic toner can be fixed under cold pressure and has a positive charging characteristic, and the sleeve is provided with a negative DC current. A reversal development method characterized by applying a voltage. 2 The amount of triboelectric charge of the magnetic toner is 2 to 20 μc/g,
The reversal developing method according to claim 1, wherein the charging voltage on the sleeve is 5 to 60V.